Project Summary/Abstract The conference will be held October 11-16, 2020 in La Paz, capital of Baja California Sur, in Mexico. This conference is held every two years, and is the only major international scientific event focused on the research and management of harmful algae events. Typically, there are 500-600 participants from 50-60 countries. Harmful algal blooms (HABs) are a major natural disturbance in marine and freshwater ecosystems that impact public health, fish and shellfish consumers and producers, drinking water supplies, and ecosystems in affected regions. The ICHA 2020 scientific program will foster discussions among HAB researchers and managers from around the world, thereby facilitating collaborations among participants within and across disciplines for the advancement of the HAB field. While the major causative organisms of multiple human poisoning syndromes (e.g., the genera Alexandrium, Dinophysis, Pyrodinium, Gymnodinium and Pseudo-nitzschia for marine systems, and Anabaena, Aphanizomenon and Microcystis for freshwater systems) continue to thrive in our waters, significant advances have been made in monitoring for these species and their toxins and in managing their human health and economic impacts, which are indeed diverse. Among the human health problems are the paralytic, diarrhetic, amnesic, neurotoxic, and azaspiracid shellfish poisoning syndromes (PSP, DSP, ASP, NSP, and AZP respectively, as well as ciguatera fish poisoning (CFP) and a range of poisoning problems cause by freshwater cyanobacteria. Over the last few decades, however, environment and anthropogenic stressors have increased, driving significant changes in our coastal and freshwater systems. Therefore, our ability to detect and manage impacts from novel or emerging organisms and their toxins is of critical importance, as is the need to manage the more established problems. The societal impacts of harmful algae are multiple and do not simply concern fisheries and aquaculture and human health, but increasingly affect other sectors, including tourism, shipping, desalination, and renewable energy supplies. Therefore, there is a continuing need to translate fundamental science into knowledge to help overcome these significant and growing societal challenges. This goal is reflected in the theme of this conference From Basic Studies to Future Applications?. Multiple thematic sessions will showcase important scientific advances and highlight impacts of harmful algae in a world of rapid change and complex interactions. Participation by scientists and managers from dozens of countries around the globe, especially developing countries, will facilitate the exchange of information on recent advances and foster international strategies for mitigating the effects of HABs.